Relay control circuit



y T958 E. DE FAYMOREAU 2,833,967

' RELAY CONTROL CIRCUIT Filed Nov. 8, 1955 INPU T VOL TA (7E INVENTOR ETIENNE 0f FAYMUREAU ATTORNEY United States Patent national Telephone and Telegraph Corporation, Nutley, N. J a corporation of Maryland Application November 8, 1955, Serial No". 545,611

7 Claims.- or. 317-149 This invention relates to a relay control circuit and particularly one adapted to energize a relay whenever an input signal voltage lies between two predetermined levels.

Many uses exist for circuits of the type to which this invention relates. For example, many types of equipment can operate and many processes can occur, onlywhile the operating temperature is between predetermined limits. By changing the temperature readings" into voltage readings, a relay control system of the present type may be employed to operate the equipment, or to carry out the process, within the prescribed temperature range. A circuit of the present type may also be employed as a timer by translating the passagejof time into a continuously rising or falling voltage (i. e., using, for example, the charge or discharge time of a condenser in an R.-C. circuit), and using the relay control circuit to mark the duration of the period byturning' on the relay during the desired period. Another use of such a relay control system is the translation of continuously rising or falling voltages into pulsesof a predetermined width, the pulses being produced during the time the relay is energized by a D. C. voltage flowing through the relay contacts. Numerous other uses of such a relay control circuit will be apparent.

In controlling the energization of a relay between two limits of an input voltage, a threshold device is required to prevent energization of the relay below the lower limit and a cutoff device is required to cut oil? energy from the threshold device to the relay when the input voltage exceeds the upper limit. It will thus be seen that two different functions and two different devices would apparently be required for so controlling a relay. It Will also be recognized that it is' desirable to adjust or vary the two levels in a simple manner.

An object of the present invention is the provision of a simple relay control circuit for energizing a relay when the input voltageis between predetermined limits.

Another object of the present invention is the provision of a circuit of the type above-described using only a single electron discharge device.

Other and further objects of the present invention will become apparent, and the foregoing will be better understood with reference to the following description of an embodiment thereof, reference being had to the drawings, in which:

Fig. l is a schematic diagram of a relay control circuit in accordance with thepresent invention; and

Fig. 2 is a curve used in explaining the operation thereof.

In carrying out my invention, I employ a multigrid tube, such as a pentode, which serves both as a threshold device and a cutoff device. The relay to be controlled is placed in the anode circuit. The input signal is applied to a first grid. A voltage divider is connected at a first point to the cathode and at a second, more positive, point to a second grid. The biasing voltage from the 2,833,967 Patented May 6-," 1958 voltage divider on the cathode serves as a threshold and prevents current flow past the first grid until the input voltage is above the bias level on the cathode. Assoon as the input signal approaches the threshold or first (lower) level, current flows past the first grid, the second grid, and the third grid to the anode, and actuates the relay. The cathode has one resistor of the voltage divider in series between it and ground. Consequently, as the input voltage continues to rise, the current through the tube increases and thereby produces an increased potential across the cathode resistor. Thus, as the input voltage rises, the voltage on the cathode also rises until it becomes greater than the fixed bias voltage applied to the third grid. At this point of the rise of the input voltage, the third grid becomes negative with respect to the cathode and thereby cuts off current to the anode, thereby de-energizing the relay. The current continues to flow from the cathode to the second grid keeping the cathode voltage above the third grid fixed bias.

Referring now specifically to the details illustrated in the drawings, an input voltage is applied via line 1 across a resistor 2, which is connected to ground, to the first grid 3 of a pentode 4, having the coil 5 of a relay 6 in series with the anode 7 thereof. A voltage divider 8 connected between a positive source of voltage 9 and ground 10 in cludes three resistors 11, 12 and 13 tapped at intermediate points 14 and 15. The cathode 16 is connected to tap 15 and the second grid 17 is connected to tap point 14. A third grid 18 is connected to a fixed potential source 19.

The value of the bias voltage applied from the voltage divider to the cathode 16 is sufficient to maintain the tube cutoff until the input voltage applied to the first grid 3 overcomes such bias. This is illustrated in Fig. 2 in which the on-oil? condition of the relay is plotted against input voltage. Assuming that the initial bias voltage applied to cathode 16 by the voltage divider 8 is 20 volts, it will be seen that no current will flow past the first grid 3 until the input voltage applied thereto is about 20 volts or over. The bias voltage applied to the second grid 17 from the voltage divider is higher than that applied to the cathode and current flows past the second grid 17. The fixed bias applied to the third grid 18 is substantially higher than the initial voltage applied to the second grid 17 so current flows past the third grid also and on to the anode, energizing relay 6. As the current fi'ow through tube 17 increases, the voltage developed across resistor 13 likewise increases, which increase is in turn applied to the second grid 17 raising the voltage of this second grid from its initial voltage of, for example, 30 volts. Assuming that the fixed voltage applied to the third grid is in this instance 40 volts, it will be seen that when the rising voltage on the cathode 16 goes above said fixed voltage (1'. e., 40 volts) the third grid will then become negative with respect to the cathode and will cut on" current how to the anode 7. The relay 6 is then deenergized. It is clear that in determining the cutoff point,

two parameters may readily be changed: one is the fixed potential 19 applied to the third grid 18, the other is the variation of the voltage fed to grid 17 with respect to the input voltage. This relation may be non-linear and may be readily changed by varying the value of the resistors in the voltage divider.

The relay 6 may have a set of front and back contacts 20 and 21 connected to difierent utilization devices 22 and 23, respectively, with the back contacts 21 being closed when the relay is tie-energized to close a circuit in device 23, while the front contacts 20 are open, opening a circuit in device 22. Upon actuation of the relay 6,

the reverse situation is produced. The precise nature of 3 the utilization device is not germane to the present invention.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A relay control circuit comprising an electron discharge device having a cathode, an anode, and a plurality of control grids, a relay having its operating coil con nected in series with said anode, means for applying a variable input voltage between a first control grid and the cathode, means for biasing the cathode to establish a threshold level for electron flow, means for applying a positive bias to the second of said control grids, and means for applying a fixed positive bias to a third of said control grids, said cathode biasing means including means responsive to the flow of current to said cathode for increasing in a positive sense the bias applied to said cathode with increases in said flow of current so as to cut oil current flow to said anode when the input voltage exceeds a given level and causes said current flow to increase above a given value.

2. A relay control circuit according to claim 1 in which the means for applying a bias to the cathode, and to the second control grid comprises a voltage divider, a source of voltage having its positive side connected to one end of said voltage divider and the negative side thereof connected to the other end of said voltage divider, and means connecting points of said voltage divider intermediate the ends thereof to said second grid and said cathode, respectively, with said second grid being connected at a more positive point.

3. A relay control circuit comprising an electron discharge device having a cathode, an anode, and a plurality of control grids, a relay having its operating coil connected in series with said anode, means for applying a variable input voltage to a first control grid, means for applying a bias to the cathode to establish a threshold level for electron flow, means for applying a more positive bias to the second of said control grids, means for applying a still more positive fixed bias to the third of said control grids whereby current flows to the anode when the input voltage exceeds said threshold level and actuates said relay, and means responsive to the flow of current to said cathode for increasing the bias of said cathode with increases in said flow of current so as to raise the cathode voltage above that of the third grid and cut off current flow to said anode when the input voltage exceeds a given level and causes said current flow to increase above a given value, the cutting off of current to the anode de-energizing said relay.

4. A relay control circuit comprising an electron discharge device having a cathode, an anode, and a plurality of control grids, a relay having its operating coil connected in series with said anode, means for applying a variable input voltage to a first control grid, means for applying a bias to said cathode to establish a threshold level for electron flow, means for applying a fixed bias to a third of said control grids, and means for applying a bias to a second of said control grids more positive than the bias on said first control grid but less than the fixed bias on said third control grid when the input voltage and resulting current flow to the cathode is below a given value whereby current fiows to said anode energizing said relay, said cathode-biasing means including means responsive to said current flow for increasing the 4' bias on said cathode to a value more positive than that of said fixed bias when said current flow exceeds said given value, to thereby cut ofi the flow of said current to the anode and de-energize said relay.

5. A relay control circuit comprising an electronic amplifying device having an electron emitter, an electron collector, and a plurality of control elements, a relay having its operating coil connected in series with said collector, means for applying a variable input voltage to a first control element, means for applying a bias to the emitter to establish a threshold level for electron flow, means for applying a fixed bias to the third of said control elements, and means for applying a bias to the second of said control elements more positive than the bias on said first control element but less than the fixed bias on said third control element when the input voltage and the resulting current flow from the cathode is below a given value whereby current flows to said collector energizing said relay, said emitter-biasing means including means for increasing the bias applied to said emitter with increases in said flow of current so that said emitter voltage exceeds the voltage on said third control element and cuts off current flow to said collector when the input voltage and said current flow exceeds said given value, to thereby de-energize said relay.

6. A control circuit for causing electron flow in accordance with predetermined input voltage levels comprising an electron discharge device having a cathode, an anode, and at least a first, second and third control grid disposed between said cathode and said anode according to ascending notation from said cathode, means for biasing said cathode to establish a threshold level for said electron flow, means for applying said input voltage to bias said first control grid above and below said threshold level, means for biasing positively said second control grid such that an increase in electron flow through said electron discharge device causes an increase in said second control grid bias, means for applying a fixed positive bias to said third control grid, and said cathode biasing means including means responsive to said electron flow through said electron discharge device for increasing the bias applied to said cathode with increases in said electron flow so as to cut off said electron flow to said anode when said input voltage exceeds a given level.

7. A control circuit for causing electron flow in accordance with predetermined input voltage levels comprising an electron discharge device having a cathode, an anode, and at least a first, second and third control grid disposed between said cathode and said anode according to ascending notation from said cathode, means for biasing said cathode to establish a threshold level for said electron flow, means for applying said input voltage to bias said first control grid above and below said threshold level, means for biasing in a positive sense said second control grid such that an increase in electron flow to said cathode causes an increase in said second control grid bias, means for applying a fixed positive bias to said third control grid, and said cathode biasing means responsive to said electron flow to said cathode for increasing the bias applied to said cathode with increases in said electron flow so as to cut off said electron flow to said anode when said input voltage exceeds a given level.

References Cited in the file of this patent UNITED STATES PATENTS 

